These studies are designed to demonstrate and characterize the cellular immune response of man to Salmonella immunization and natural infection. The phagocytic and bactericidal activity of immune macrophages will be quantitated. The specificity of this activity and the role of specific opsonins will be investigated. The influence of soluble mediators from stimulated lymphocytes on the mobility and bactericidal activity of human phagocytic cells will be evaluated. These investigations will involve the use of macrophage monolayers, lymphoid cell lines, radioactive bacteria, commercial and prepared antigens and standard bacteriologic techniques. The information obtained will not only contribute to our understanding of the pathogenesis of Salmonella infections and provide a more rational basis for developing and testing human Salmonella vaccines, but may also be useful as a model for the study of human intracellular bacterial infections.